Valve does nothing to suppress competition (it can’t really either)
They at least used to have a rule that publishers can’t sell cheaper on other platforms (outside of timed sales that is), meaning that consumers can’t get a better price on other storefronts even when those platforms would take a smaller cut. That was very much suppressing the competition as them taking smaller cuts can’t transfer into cheaper prices if the publisher also wanted to sell on Steam.
Well, they are allegedly forcing price parity on publishers, so they can’t sell cheaper on their own website or some other storefront that takes smaller cuts. That’s anticompetitive as shit, and they are being sued over it.